Conventionally, in a large-sized liquid crystal display apparatus for an active matrix display, a horizontal drive circuit and vertical drive circuit incorporating driver ICs for applying a predetermined voltage to the pixels are provided by TAB (tape automated bonding) or COG (chip on glass) at the outside of the substrate of the liquid crystal display panel. Further, in a small-sized liquid crystal display apparatus, the horizontal drive circuit is provided outside the substrate of the liquid crystal display panel, while the vertical drive circuit is provided integrally in the substrate of the liquid crystal display panel.
Aging is performed for displaying a predetermined image on the liquid crystal display panel to examine for defects in the panel itself before assembling the liquid crystal display panel into a liquid crystal display apparatus.
However, with a liquid crystal display panel to which external drive circuits are connected by TAB, COG, etc., it is not possible to display an image unless the external drive circuits are connected to the liquid crystal panel. Therefore, aging cannot be performed by the liquid crystal panel alone.
Therefore, there is an inconvenience that drive circuits have to be incorporated in advance as a module in order to perform aging. Furthermore, when the aging reveals any defect, reuse of the TAB, COG, or other circuits incorporated as a module requires that they be removed from the defective panel. This is troublesome. Thus, there was a problem that the work efficiency of aging was low in such liquid crystal display panels.
Also, as explained above, in a large-sized liquid crystal display apparatus for an active matrix display, the horizontal drive circuit and vertical drive circuit incorporating driver ICs for applying a predetermined voltage to the pixels are provided outside the substrate of the liquid crystal display panel by TAB, COG, etc. In this case, there is normally a one-to-one correspondence between the outputs of the external driver IC and source lines of the liquid crystal display panel. The output voltages from the output terminals of the driver ICs are supplied as they are to the corresponding source lines.
On the other hand, in a small-sized liquid crystal display apparatus for active matrix display, a time sharing drive method (selector method) is employed, the horizontal drive circuit is provided as an external circuit, and the vertical drive circuit is integrally provided in the substrate of the liquid crystal display panel.
In the time sharing drive method, a plurality of source lines are treated as one unit, and signals given to the plurality of source lines in a unit are output from the driver IC in a time series. In a liquid crystal display panel, a plurality of source lines are treated as one unit and a time sharing switch is provided, and signals in a time series output from a driver IC are divided in time by the time sharing switch and successively given to the plurality of source lines.
According to the time sharing drive method, the outputs of the driver IC of the external horizontal drive circuit and source lines of the liquid crystal display panel are not in a one-to-one correspondence. For example, a write operation is performed on three source lines by one output line of the driver IC. Accordingly, the number of output pins of the driver IC can be reduced by using the time sharing drive method.
However, in a medium-sized to small-sized liquid crystal display panel used in a PDA etc., the time sharing drive method causes the following problems:
First, since a horizontal writing time is divided in the time sharing drive method, a sufficient writing time to the source lines from the driver IC cannot be secured.
Second, a horizontal drive frequency of the driver IC has to be made higher in accordance with the number of divisions of one horizontal scanning period. For example, when dividing one horizontal scanning period into three equal portions, the driver IC has to operate at three times the horizontal drive frequency of the liquid crystal.
Third, since a pulse is required to make the time sharing switch operate and data has to be rearranged to change the order of writing to the source lines, medium-sized to small-sized liquid crystal display panels require a large power consumption and a memory for rearranging data. These are also problems.
On the other hand, a drive method relying on external circuits for both of the horizontal drive circuit and vertical drive circuit suffers from the problem that with medium-sized to small-sized liquid crystal display panels, it is not possible to take out terminals from one side of the panels. Therefore, the problems arise that the outside shape of a module becomes large and assembly of the module becomes complicated. Furthermore, the number of connection points of the liquid crystal display panel and the outside becomes large, so the probability of a connection defect arising becomes higher.